Electronic devices usually require a certain available amount of power for functioning correctly. Some systems, for example, safety critical systems, such as for example vehicles, or systems therein, for example automotive safety critical systems, such as car braking systems, may not be fault tolerant and may employ fault tolerant or fail-safe circuits or devices, which, in an event of failure, respond such that only a minimum or no harm is caused to the system, the environment and users of the system.
In order to specify functional safety, for example for automotive applications, standards are defined by standardization organizations, such as the IEC 61508 standard by the International Electrotechnical Commission (IEC) or the ISO 26262 functional safety standard by the International Organization for Standardization. For example, for safety applications targeting Automotive Safety Integrity Level D (ASIL-D), i.e., the highest level of functional safety defined in ISO 26262, the safety functions must be ensured even in case of a power supply loss. In an integrated circuit (IC), power supply loss may, for example, be caused by a pin lift or a bonding disconnection.
As shown in FIG. 1, a prior art power safety circuit 10 may provide a solution for increased fault tolerance by means of power supply redundancy. The shown prior art circuit protects a fail safe output terminal 12 driven by an output terminal driver circuit 14 in a fail safe machine 16, wherein the output terminal driver circuit 14 is supplied with power from a first and a second power source 18, 20 at the same time through two redundant power supply terminals 22, 24, both connected to supply the output terminal driver circuit 14 with power. For example, in U.S. Pat. No. 5,745,670, fault tolerance of an electronic system against power supply loss is achieved by providing power from two power sources via two redundant power supply connections to a local power supply and a power distribution bus.